A pump assembly for concrete-like masses is known which has a hopper adapted to hold the mass and having a front wall formed with a front port and a rear wall formed with two rear ports. Respective piston pumps secured to the rear wall outside the hopper over the rear ports can draw portions of the mass out of the hopper and expel the drawn-out portions back into the hopper through the respective rear ports. An outlet conduit is connected to the front wall outside the hopper over the front port. A nonstraight distributor pipe in the hopper has a front end engaged over and aligned with the front port, and a rear end engageable over and alignable with either of the rear ports. Such an assembly has means for pivoting the distributor pipe about the front axis between a position with the rear end aligned with and engaged over one of the rear ports and the other rear port exposed in the hopper and another position with the rear end aligned with and engaged over the other rear port and the one rear port exposed in the hopper. Thus this distributor pipe oscillates back and forth synchronously with the pumps to deliver a nearly continuous flow to the outlet conduit. As one pump is expelling its contents into the distributor pump, the other pump is sucking in a new load directly from the hopper, then the distributor pipe swings over and the pumps reverse.
German Pat. No. 1,285,319 and German patent document 1,653,607 describe such a system. The distributor pipe in these arrangements is S-shaped, so that extensions from the front and rear ends of the centerline of the pipe are parallel but laterally offset from each other. This double bend in the distributor pipe leads, obviously, to greater resistance to flow. Hence the head of such a pump assembly is limited. Otherwise the pumps have to be overdimensioned to overcome this nonproductive deflection of flow.
Such a pump is also disadvantageous when permanently mounted on a concrete-pumper truck. Normally the pump assembly is mounted on the chassis and the concrete is pumped into a pipe that extends centrally out from a distributor post. Substantial piping is necessary for the pump assembly to be hooked up in such an arrangement. Obviously conducting the concrete unnecessarily through such piping represents a serious waste of energy.